In dentistry, die models of teeth and jaw portions are often used for making complex prosthodontic appliances, such as bridgework, crowns, and the like. This is accomplished by making an impression mold out of a quick-setting impression material around the actual teeth of the patient, thus duplicating the patient's anatomical structure. Thereafter, models of the teeth and jaw portions are reproduced from the impression, which is then utilized in the building of the dental prosthesis.
In a typical procedure, after preparation of the model, several dowel pins, typically made of brass, are inserted into the base of the model to permit the cutting of various portions of the model into sections, at least one dowel pin fitting into each section.
To facilitate the cutting of the model into sections, prior to cutting, in conventional practice, the model is placed onto a mass of partially cured dental stone which has been formed into a lump on a flat surface, and is of about the consistency of dough. The dowel pins are forced into the dental stone, and the bottom surface of the model rests on the upper surface of the dental stone. Thereafter, the dental stone is allowed to harden, after which it is ground into an appropriate configuration for being received by an articulator, usually roughly approximately the shape of the die model, for duplication of jaw action as the dental prosthetis is built on the model.
After hardening of the stone, the model can be cut into various separate sections as desired. The model is generally treated with a separating medium (releasing agent) to prevent adhesion to the dental stone. Accordingly, the individual separated portions of the model, each carrying one or more dowel pins, can be selectively removed from the mass of stone and the rest of the model, for work. Thereafter, it may be replaced, being positioned and retained by the one or more dowel pins attached to it by reinsertion of the dowel pins into their holes in the dental stone, to precisely reposition the separate model portion with respect to the rest of the model.
The above conventional prior art technique of preparing dental models for work is tedious and time consuming, requiring considerate skill in the proper preparation of a hand-shaped mass of dental stone for receiving the model.
Also, in this technique, one must be very careful to avoid creating bubbles in the uncured dental stone adjacent to the dowel pins, or under the model, which, of course, would reduce the firm mounting of the model in the stone.
Furthermore, the working time of the dental stone, being partially cured to the consistency of dough when it is generally worked and shaped, may be undesirably short under certain circumstances. This may result in the need to reprepare the dental stone, and repeat the operation.
Furthermore, problems exist, in that it is often desirable to permanently retain some portions of the model in the stone, when there is no need to remove it, to avoid the possibility that those portions of the model may accidentally fall out or get lost. On the other hand, other portions of the model should be removable, as described above.
Another problem that arises in the grinding of the dental stone to fit articulator: if one accidentally grinds the end of a dowel pin, which is typically made of brass or other soft alloy, the end of the dowel pin may be flared outwardly by the force of the grinding. Thus it becomes impossible to remove from the stone the particular section of the model to which that dowel pin is attached without laborous further grinding and cutting away (or rebending) of the accidentally flared end of the dowel pin.